This invention relates to a dye and a dye carrier ink ribbon for thermal dye transfer system hard copy which is suitably adapted for use, for example, as a color hard copying material of video printers.
In video printers, it is recently practiced to form a dye carrier ink ribbon by coating disperse dyes dissolved in hydrophobic high molecular weight materials on a ribbon substrate and form an image by causing thermal transfer of the dye from the dye carrier ink ribbon to a second hydrophobic high molecular weight material provided on an acceptor sheet such as a synthetic paper, wherein the thermal transfer of the dye is controlled according to a video signal to be printed synthetic paper. It will be noted that although it has been hitherto accepted as desired that the dye has sublimating properties in view of the principle of forming an image, more importance is placed on thermal diffusing properties than on the sublimating properties in view of a recent trend of investigations wherein the types of materials used therefor a taken into consideration.
The reason why disperse dyes are employed for this purpose is based on the fact that the disperse dye is hydrophobic in nature and the ink ribbon is appropriately fixed to a substrate, with a good practical sensitivity at the time of the transfer.
However, when disperse dyes are used as a dye for ink ribbons, there arises the problem that the sensitivity, hue and light fastness are not always satisfactory at the time of the transfer.
On the other hand, there are known cationic dyes which have good brightness inherent to basic materials and high coloring properties and which are used as a dye for acrylic fibers. The dye may be applied to as a dye for ink ribbons for the hard copy. Although cationic dyes exhibit good light fastness and wet fastness on acrylic substrates, they have hydrophilicity, so that it is difficult to stably, uniformly fix on a resin such as polyethylene terephtalate (PETP) which is ordinarily used as a substrate of ribbon. Thus, it is not possible to form an ink ribbon for thermal transfer by the use of cationic dyes.